The invention relates to the correction or reduction of distortion in captured images, for example images captured by a camera. In particular it relates to the correction of distortion for text images, which may be subsequently subjected to electronic character recognition.
The immense proliferation of hand-held devices with cameras in the present consumer market naturally invokes an interest to utilize these cameras for diverse applications at times not originally intended.
One such application is the use of such cameras for document imaging and thereby pushing the limits of the device to replace document scanners.
Due to the limited optics present in hand-held cameras, the captured images of documents exhibit perspective and some radial distortions. In addition, the images appear mostly skewed. These pose severe problems to a document processing system for handheld camera images, and hence significantly decrease the performance of the system.
There has been some interest towards the problem of perspective correction for document images in the past. Most approaches proposed extract illusory perspective cues in document images and use these cues to rectify the perspective distortion in the document image. Although these methods do not require a complete view of the document, they assume ends of the justified text to be present in the view.
The known approaches are therefore often not satisfactory for perspective correction when the image does not have a complete view of the printed lines but has only a partial view of the page. In a partial view, the ends of the printed lines may not be visible and so perspective cues can not be easily obtained from the image.